Re: mm: BUG in expand_downwards

[Dmitry Vyukov]

On Wed, Jan 27, 2016 at 1:24 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> On Wed, Jan 27, 2016 at 12:49 PM, Konstantin Khlebnikov
> <koct9i@xxxxxxxxx> wrote:
>> It seems anon_vma appeared between lock and unlock.
>>
>> This should fix the bug and make code faster (write lock isn't required here)
>>
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -453,12 +453,16 @@ static void validate_mm(struct mm_struct *mm)
>>         struct vm_area_struct *vma = mm->mmap;
>>
>>         while (vma) {
>> +               struct anon_vma *anon_vma = vma->anon_vma;
>>                 struct anon_vma_chain *avc;
>>
>> -               vma_lock_anon_vma(vma);
>> -               list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
>> -                       anon_vma_interval_tree_verify(avc);
>> -               vma_unlock_anon_vma(vma);
>> +               if (anon_vma) {
>> +                       anon_vma_lock_read(anon_vma);
>> +                       list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
>> +                               anon_vma_interval_tree_verify(avc);
>> +                       anon_vma_unlock_read(anon_vma);
>> +               }
>> +
>>                 highest_address = vma->vm_end;
>>                 vma = vma->vm_next;
>>                 i++;
>
>
> Now testing with this patch. Thanks for quick fix!


Hit the same BUG with this patch.
Please try to reproduce it locally and test.


>> On Wed, Jan 27, 2016 at 1:51 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>>> Hello,
>>>
>>> The following program trigger BUG in expand_downwards (run it in tight
>>> parallel loop for a while):
>>>
>>> // autogenerated by syzkaller (http://github.com/google/syzkaller)
>>> #include <pthread.h>
>>> #include <stdint.h>
>>> #include <string.h>
>>> #include <sys/syscall.h>
>>> #include <unistd.h>
>>>
>>> long r[10];
>>>
>>> void* thr(void* arg)
>>> {
>>>   switch ((long)arg) {
>>>   case 0:
>>>     r[0] = syscall(SYS_mmap, 0x20731000ul, 0x2000ul, 0x2ul, 0x22132ul,
>>>                    0xfffffffffffffffful, 0x0ul);
>>>     break;
>>>   case 1:
>>>     r[1] = syscall(SYS_mremap, 0x20732000ul, 0x1000ul, 0x3000ul, 0x3ul,
>>>                    0x2015b000ul, 0);
>>>     break;
>>>   case 2:
>>>     r[2] = syscall(SYS_fanotify_init, 0x20ul, 0x40002ul, 0, 0, 0, 0);
>>>     break;
>>>   case 3:
>>>     r[3] = syscall(SYS_mremap, 0x2015c000ul, 0x1000ul, 0x4000ul, 0x3ul,
>>>                    0x204eb000ul, 0);
>>>     break;
>>>   case 4:
>>>     r[4] = syscall(SYS_munlock, 0x204eb000ul, 0x4000ul, 0, 0, 0, 0);
>>>     break;
>>>   case 5:
>>>     r[5] = syscall(SYS_mremap, 0x204ec000ul, 0x1000ul, 0x1000ul, 0x3ul,
>>>                    0x2015d000ul, 0);
>>>     break;
>>>   case 6:
>>>     r[6] = syscall(SYS_mmap, 0x20000000ul, 0x1000ul, 0x3ul, 0x32ul,
>>>                    0xfffffffffffffffful, 0x0ul);
>>>     break;
>>>   case 7:
>>>     r[7] = syscall(SYS_sigaltstack, 0x204ec000ul, 0x20000000ul, 0, 0, 0,
>>>                    0);
>>>     break;
>>>   case 8:
>>>     memcpy((void*)0x2015bffa, "\x2e\x2f\x62\x75\x73\x00", 6);
>>>     r[9] = syscall(SYS_mkdir, 0x2015bffaul, 0x108ul, 0, 0, 0, 0);
>>>     break;
>>>   }
>>>   return 0;
>>> }
>>>
>>> int main()
>>> {
>>>   long i;
>>>   pthread_t th[9];
>>>
>>>   srand(getpid());
>>>   memset(r, -1, sizeof(r));
>>>   for (i = 0; i < 9; i++) {
>>>     pthread_create(&th[i], 0, thr, (void*)i);
>>>     usleep(1000);
>>>   }
>>>   for (i = 0; i < 9; i++) {
>>>     pthread_create(&th[i], 0, thr, (void*)i);
>>>     usleep(rand()%1000);
>>>   }
>>>   usleep(10000);
>>>   return 0;
>>> }
>>>
>>>
>>>
>>> =====================================
>>> [ BUG: bad unlock balance detected! ]
>>> 4.5.0-rc1+ #292 Not tainted
>>> -------------------------------------
>>> a.out/7506 is trying to release lock (&anon_vma->rwsem) at:
>>> [<     inline     >] vma_unlock_anon_vma include/linux/rmap.h:123
>>> [<ffffffff816f8e5d>] validate_mm+0x12d/0x850 mm/mmap.c:461
>>> but there are no more locks to release!
>>>
>>> other info that might help us debug this:
>>> 1 lock held by a.out/7506:
>>>  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff8127dfd7>]
>>> __do_page_fault+0x737/0x960 arch/x86/mm/fault.c:1184
>>>
>>> stack backtrace:
>>> CPU: 1 PID: 7506 Comm: a.out Not tainted 4.5.0-rc1+ #292
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>>  00000000ffffffff ffff88005d107b50 ffffffff829e79ad ffff8800603b4ce8
>>>  ffff88005f15df00 ffffffff816f8e5d ffff88005d107b80 ffffffff81450884
>>>  ffff8800603b4ce8 ffff88005f15e720 ffff88005f15e720 00000000ffffffff
>>> Call Trace:
>>>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>>>  [<ffffffff829e79ad>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>>>  [<ffffffff81450884>] print_unlock_imbalance_bug+0x174/0x1a0
>>> kernel/locking/lockdep.c:3261
>>>  [<     inline     >] __lock_release kernel/locking/lockdep.c:3385
>>>  [<ffffffff8145c687>] lock_release+0x937/0xce0 kernel/locking/lockdep.c:3606
>>>  [<ffffffff814490ba>] up_write+0x1a/0x60 kernel/locking/rwsem.c:91
>>>  [<     inline     >] vma_unlock_anon_vma include/linux/rmap.h:123
>>>  [<ffffffff816f8e5d>] validate_mm+0x12d/0x850 mm/mmap.c:461
>>>  [<ffffffff817034be>] expand_downwards+0x19e/0xb30 mm/mmap.c:2283
>>>  [<ffffffff81703ecb>] expand_stack+0x7b/0xe0 mm/mmap.c:2338
>>>  [<ffffffff8127df88>] __do_page_fault+0x6e8/0x960 arch/x86/mm/fault.c:1217
>>>  [<ffffffff8127e358>] trace_do_page_fault+0xe8/0x420 arch/x86/mm/fault.c:1331
>>>  [<ffffffff8126f514>] do_async_page_fault+0x14/0xd0 arch/x86/kernel/kvm.c:264
>>>  [<ffffffff8645bdf8>] async_page_fault+0x28/0x30 arch/x86/entry/entry_64.S:986
>>>  [<     inline     >] SYSC_sigaltstack kernel/signal.c:3157
>>>  [<ffffffff8138600c>] SyS_sigaltstack+0x6c/0x90 kernel/signal.c:3155
>>>  [<ffffffff86459ab6>] entry_SYSCALL_64_fastpath+0x16/0x7a
>>> arch/x86/entry/entry_64.S:185
>>> mmap: free gap 1000, correct 0
>>> mm ffff8800603a4e00 mmap ffff88005fc794c0 seqnum 12 task_size 140737488351232
>>> get_unmapped_area ffffffff811af470
>>> mmap_base 140584500215808 mmap_legacy_base 47048170172416
>>> highest_vm_end 140737437655040
>>> pgd ffff88005fc20000 mm_users 2 mm_count 1 nr_ptes 25 nr_pmds 3 map_count 49
>>> hiwater_rss 7 hiwater_vm 813a total_vm 913e locked_vm 2
>>> pinned_vm 0 data_vm 902e exec_vm d1 stack_vm 2a
>>> start_code 400000 end_code 4ce986 start_data 6cee90 end_data 6d0d88
>>> start_brk 934000 brk 957000 start_stack 7ffffcf5e660
>>> arg_start 7ffffcf5feae arg_end 7ffffcf5feb6 env_start 7ffffcf5feb6
>>> env_end 7ffffcf5fff0
>>> binfmt ffffffff8797c260 flags cd core_state           (null)
>>> ioctx_table           (null)
>>> owner ffff88005d99df00 exe_file ffff880033321680
>>> mmu_notifier_mm           (null)
>>> flags: 0x0()
>>> ------------[ cut here ]------------
>>> kernel BUG at mm/mmap.c:481!
>>> invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
>>> Modules linked in:
>>> CPU: 1 PID: 9534 Comm: a.out Not tainted 4.5.0-rc1+ #292
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>> task: ffff880031522f80 ti: ffff8800314f8000 task.ti: ffff8800314f8000
>>> RIP: 0010:[<ffffffff816f922c>]  [<ffffffff816f922c>] validate_mm+0x4fc/0x850
>>> RSP: 0018:ffff8800314ffc60  EFLAGS: 00010286
>>> RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000000
>>> RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffffed000629ff22
>>> RBP: ffff8800314ffcc8 R08: 0000000000000001 R09: 0000000000000000
>>> R10: 0000000000000003 R11: 1ffffffff12e43c4 R12: 0000000000000031
>>> R13: 0000000000000000 R14: 00007ffffcfa4000 R15: dffffc0000000000
>>> FS:  00007fdc59313700(0000) GS:ffff88003ed00000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>> CR2: 00000000204ec000 CR3: 000000005fc20000 CR4: 00000000000006e0
>>> Stack:
>>>  0000000000486f70 ffff8800603a4e60 ffff8800603a4e00 0000003100000001
>>>  0000000000000000 0000000000041000 ffff88005fc78538 ffff88005fc78530
>>>  ffff880032870a60 0000000000000000 ffff880031e61e00 000000001f6a9000
>>> Call Trace:
>>>  [<ffffffff817034be>] expand_downwards+0x19e/0xb30 mm/mmap.c:2283
>>>  [<ffffffff81703ecb>] expand_stack+0x7b/0xe0 mm/mmap.c:2338
>>>  [<ffffffff8127df88>] __do_page_fault+0x6e8/0x960 arch/x86/mm/fault.c:1217
>>>  [<ffffffff8127e358>] trace_do_page_fault+0xe8/0x420 arch/x86/mm/fault.c:1331
>>>  [<ffffffff8126f514>] do_async_page_fault+0x14/0xd0 arch/x86/kernel/kvm.c:264
>>>  [<ffffffff8645bdf8>] async_page_fault+0x28/0x30 arch/x86/entry/entry_64.S:986
>>>  [<     inline     >] SYSC_sigaltstack kernel/signal.c:3157
>>>  [<ffffffff8138600c>] SyS_sigaltstack+0x6c/0x90 kernel/signal.c:3155
>>>  [<ffffffff86459ab6>] entry_SYSCALL_64_fastpath+0x16/0x7a
>>> arch/x86/entry/entry_64.S:185
>>> Code: 58 60 44 39 e3 74 73 e8 03 0f e7 ff 44 89 e2 89 de 48 c7 c7 a0
>>> dc 5a 86 e8 e7 c3 f4 ff e8 ed 0e e7 ff 48 8b 7d a8 e8 24 00 fe ff <0f>
>>> 0b e8 dd 0e e7 ff 8b 55 b4 44 89 e6 48 c7 c7 40 dc 5a 86 e8
>>> RIP  [<ffffffff816f922c>] validate_mm+0x4fc/0x850 mm/mmap.c:481
>>>  RSP <ffff8800314ffc60>
>>> ---[ end trace 5282aed32b3391b4 ]---
>>>
>>>
>>> And there seems to be some locking issue in validate_mm.
>>>
>>> On commit 92e963f50fc74041b5e9e744c330dca48e04f08d (Jan 24).